This is our packing list from our 3 night, 4 day backpacking trip to Havasupai. This was an 11 mile hike through the desert to a waterfall oasis, so if you're packing for a colder trip make sure you factor in the extra weight of heavier layers! Also, if you're hiking as a couple, notice that Matt always takes a heavier pack than I do because he's nice...and he knows I would take forever to make it up the mountain with that extra weight! Buying gear can be expensive up front, but once you have everything, it will last you forever!
We highly recommend heading in to REI to get sized for your hiking bag. Having a comfortable pack will make or break your trip, and with so many options out there it's best to try it before you buy it! I have an unusually short torso and after trying all the bags at the store, the Gregory pack size XS was the only one that fit me. Matt had a much easier time finding his though!